Abstract:
Abstract: Curing has important functions in meat products, which contributes positively to the structural and sensory characteristics of the meat. By various curing methods, a wide variety of cured meat products are produced. Considering the processing time or the weight ratio of brine to meat needed to obtain a product with better characteristics from a sensorial or a structural point of view, neither scientists nor manufacturers came to a similar standpoint. Nowadays, to some extent, reducing curing time and improving the curing operations may be achieved through tumbling or other methods. From a production perspective, fast tumbling can shorten processing time and is favorable, but it can lead to more heat production and products of poor quality. Ultrasound is a novel processing technology which may accelerate mass transfer through the mechanism of cavitation in meat tissue. Ultrasound is also favorable from an eating point of view since it results in more tender and juicy meat. In order to explore novel curing processing for shortening curing time and improving product quality, we assessed the effects of pressure-transform tumbling curing assisted with ultrasound (PTU) technique on the protein secondary structures, moisture distribution and microstructure of chicken. For this purpose, fresh chicken breasts were selected (50±1 g, 5 cm × 5 cm × 2 cm) and treated at 4 ℃ for 100 min with one of the 3 following curing treatments: (1) static brining, (2) vacuum tumbling (VT) (rotation speed of 16 revolutions per minute, 0.08 MPa, 100 min, 15 minutes of continual work and then 5 minutes of resting period), or (3) pressure-transform tumbling assisted with ultrasound (40 kHz, 140 W; parameter setting was consistent with the VT curing, and the only difference was the ultrasound treatment of the meat samples carried out by activating ultrasonic probe during the resting period). The ratio of meat weight to brine weight was 100: 30 (g/mL) for all treatments. The brine solution was composed of 2% NaCl, 0.3% compound phosphates, 250 mg/kg sodium ascorbate and 150 mg/kg sodium nitrite (relative to meat weigh). The results showed that the proportion of α-helix was reduced greatly (P<0.05), and the amount of β-sheet and β-turn were increased (P<0.05) after PTU treatment. The LF-NMR (low-field nuclear magnetic resonance) data indicated that the transverse relaxation time of the bound water (T21) and immobilized water (T22) was clearly reduced by PTU compared with VT and static brining. Moreover, the proportion of peak area of T21 was significantly increased (P<0.05) for PTU treatment, which indicated that the water molecules were combined with protein more tightly and part of free water was turned into immobilized water. SEM (scanning electron microscopy) and TEM (transmission electron microscope) showed that PTU could result in severe degradation of myofibril and larger distance between muscle fibers compared to static brined or VT samples. Based on this study one can conclude that PTU treatment can serve as a useful alternative to tumbling for improving curing in meat tissue as well as enhancing water-holding capacity and textural properties. The research provides a theoretic basis and practical application reference for the PTU technology in the meat industry and related equipment design.